Oceanica Beds Research Articles

Spatio-temporal variability of Borer Polychaetes in Posidonia oceanica beds and its relation to meadow structure

Posidonia oceanica forms an extremely productive and complex ecosystem in the coastal Mediterranean Sea providing a suitable habitat for hundreds of plant and animal species. Among motile invertebrates associated to Posidonia meadows, polychaete borers of the plant sheaths represent a unique group which exploit a peculiar microhabitat. They belong to the family Eunicidae with three dominant species, Lysidice collaris, L. ninetta and L. unicornis. Due to their strong association with Posidonia shoots, these animals are particularly suitable to study the plant and animal spatial relationships and their pattern of variability. The aim of this work was to evaluate the frequency of occurrence of these animals (Index of Borer, IB) at different spatial and temporal (summer vs winter) scales in two Posidonia meadows off the Ischia Island (Gulf of Naples, Italy), which are exposed to different degrees of human impact and of hydrological conditions. Results showed IB values of L. collaris (the most abundant species) significantly different between meadows and at scales from 10s to 100s of meters, as well as between summer and winter. The IB of L. ninetta showed significant differences only at scales of 10s of meters while, on the contrary, the IB of L. unicornis (the less abundant species) did not show variability at any spatial and temporal scales. Most of the variance was at the more impacted and less water movement exposed meadow, suggesting higher level of small and intermediate scales of patchiness of borers at this meadow. These variation patterns are discussed in relation to local environmental differences between the studied Posidonia beds.

Reprint of “Monitoring of a Posidonia oceanica bed (Punta Manara, Eastern Ligurian Sea, Italy) and the associated molluscs twenty years after: What's new?”

This research project by the Marine Biology Laboratory at Turin University determined the degree of conservation and measured the size of the Posidonia oceanica bed in the eastern Ligurian Sea off Punta Manara in 1985–1986, a bed that had also been examined in 1973. This project assessed the structure, dynamics, and organization of the foliar stratum malacofauna in relation to the most important space–time variables, the bathymetric gradients, and the seasons. In 2006 the laboratory investigated this bed with methods like the previous ones in order to evaluate the effect of anthropogenic disturbances and to assess any changes in the P. oceanica and mollusc-community dynamics. Our overall project has spanned many years, something unique in P. oceanica studies. Our structural analysis of the meadow found (i) a reduction in shoot density in all the bed's regions, particularly in the shallow and intermediate belts; (ii) a progressive reduction of the lower limit (now considered erosive–regressive). We sampled the foliar stratum molluscs using hand-towed nets, the means we used to collect semi-quantitative data. In 2006, there were 40% fewer specimens and 31.5% more species than in 1985–1986. The core-stock (sensu Russo) has remained the same over the years in terms of both the presence and the abundance of species (8 dominant species belonging to Cerithidae and Rissoidae). As in 1985–1986, Bittium latreillii is the dominant species, whose juveniles exhibited similar settlement dynamics on the foliar strata and whose samples had comparable peaks in reproduction and abundance. The multivariate approach was applied to both the 1985–1986 and the 2006 data set. The present results confirm those obtained through the Detrended Correspondence Analysis (DCA) in 1985–1986. Namely, time (the period or the season) is the main factor of variability, the one that influences the malacological assemblages the most. The composition of the stocks depends closely on the sampling period (ANOSIM, R=0.532, P<0.001) and hence is linked to the biological cycle of the seagrass. The development of P. oceanica affects the malacological assemblages and regulates them quantitatively, something most evident in the reproductive and settlement cycles of the two dominant families, Cerithidae and Rissoidae. Thus the spatial variations (the variations in depths or bathymetric gradient) play a major role in determining the species of the stocks, while the temporal variations – the changes in seasons – play a major role in determining the total number of molluscs.

Seed photosynthesis enhances Posidonia oceanica seedling growth

Posidonia oceanica seeds demonstrate photosynthetic activity during germination as well as throughout seedling development, a fact which suggests that seed photosynthesis can influence seedling growth. This study examines the contribution of seed photosynthesis to changes in leaf and root biomass, the concentration of seed carbohydrate reserves (free sugars and starch) and elemental C, N and P content in seedlings exposed to different light/dark treatments. Green seeds attached to seedlings remained photosynthetically active for three months and photosynthetic activity in the seeds enhanced seedling growth in leaves and roots. It was estimated that ca. 29.26% of leaf biomass and ca. 42.31% of root biomass production was due to seed photosynthetic activity. Photosynthesis occurred at a higher rate in seeds than in leaves during early seedling growth, and extreme light limitation reduced the mobilization of carbon reserves stored in the seeds. These adaptations control leaf self‐shading and plant competition in well‐established P. oceanica beds while also promoting increased seedling survival rates in open, uncolonised areas where clonal growth is limited.

Wave energy and wave-induced flow reduction by full-scale model Posidonia oceanica seagrass

This paper presents results from experiments in a large flume on wave and flow attenuation by a full-scale artificial Posidonia oceanica seagrass meadow in shallow water. Wave height and in-canopy wave-induced flows were reduced by the meadow under all tested regular and irregular wave conditions, and were affected by seagrass density, submergence and distance from the leading edge. The energy of irregular waves was reduced at all components of the spectra, but reduction was greater at the peak spectral frequency. Energy dissipation factors were largest for waves with small orbital amplitudes and at low wave Reynolds numbers. An empirical model, commonly applied to predict friction factors by rough beds, proved applicable to the P. oceanica bed. However at the lowest Reynolds numbers, under irregular waves, the data deviated significantly from the model. In addition, the wave-induced flow dissipation in the lower canopy increased with increasing wave orbital amplitude and increasing density of the mimics. The analysis of the wave-induced flow spectra confirm this trend: the reduction of flow was greatest at the longer period component of the spectra. Finally, we discuss the implications of these findings for sediment dynamics and the role of P. oceanica beds in protecting the shore from erosion.

Minimizing environmental risks on constructing marine pipelines: Aguilas desalination plant

In the building of marine brine discharge pipelines from desalination plants, there are some technical and environmental conditions that require previous numerous studies to guarantee their viability. In the project of Águilas desalination plant with a production capacity of 180.000 m3/day, in Murcia, Spain, a marine emissary was designed. It was made up of various sections that entail different building complexities. The main difficulty was to build a tunnel in the rocky massif called “Peñon del Roncaor”; the tunnel was dug through a piling of 443 m of length and an exterior diameter of 2.400mm that would have come up at a depth of 12 m to join the submarine section of 290 m of length. These more detailed geotechnical studies showed a great heterogeneity in the composition of the materials to be excavated from the Peñon. In order to avoid any risk of affecting to the castle right above considered of cultural interest, a new tracing of the tunnel was designed. The new tracing runs the Peñon’s outer south borders right into the dumping area. This new tracing implies greater length of piping and greater seabed marine area occupation as well; it required carrying out additional bionomic studies to guarantee its environmental compatibility. We must bear in mind that the marine surroundings of Águilas are a protected area included in the Red Natura 2000 (LIC Submerged Costal Strip of the Murcia Region) whose predominant bionomic community is the Posidonia oceanica beds, limited to the Southwest by another less dense seagrass of Cymodocea nodosa. These seagrass meadows and rock communities suffer anthropic pressure for its proximity to the city of Águilas, as near-shore marine discharges, fishing activity, and others. And, there are other affections of natural condition: terrigenous sediments and nutrients that get to the dry riverbed name El Charco, having seriously affected the species of greater natural value and the implementation of those ubiquitous species, and thus impoverishing habitat in general. Due to the fact that P. oceanica seagrasses have very low tolerance to increased salinity in the western Mediterranean Sea; a hydrodynamic model was developed to estimate the likely dilution of the brine discharge for this new solution. Other works comprise a bathymetric survey to establish the profile of the ocean bottom—very important for pipeline construction—a sediment characterization, the study of the oceanographic conditions and a monitoring study of the marine water quality to settle the values of the water quality in the preoperation moment and the parameters needed for process designing. During the construction of the pipeline, an environmental surveillance program was developed. And at the end of the stage, a study was developed to know the impacts produced by the works carried out and to establish the “zero situation” before start of the operation phase. In addition to that, a very strict environmental legislation was applied along the process. These regulations included exhaustive and systematic controls of several environmental parameters when starting and during the plant operation.

Texture Segmentation Applied to P. Oceanica Beds’ Upper Boundary Tracking by ROVs

The paper deals with an image processing technique for texture segmentation. By way of texture segmentation, a binary image is constructed and used to fit a line of the dominant direction of propagation of the texture in the image plane. The texture is captured by an oblique angle that positions the image plane in a near vertical orientation to the sea bottom plane. The texture being recognized in the experiment is that of Posidonion Oceanicœ, the benthic community (meadow or bed) of the Neptune grass Mediterranean endemic. It is the motivation of this paper for the dominant direction of propagation of the texture segment in the image plane to be used as a measure of the true direction of propagation of the upper border of Posidonion Oceanicœ in a feedback control loop that will enable the vehicle to autonomize the task of upper border tracking. The algorithm for extraction features four distinct phases: multi-resolution analysis using wavelets, vector quantization, post-processing of the obtained binary image and the extraction of the line parameters. The classification and line-fitting procedure are computationally optimized and made more robust by using weights in the Least Squares fitting procedure, and using nonlinear binary-image domain processing.

Monitoring of a Posidonia oceanica bed (Punta Manara, Eastern Ligurian Sea, Italy) and the associated molluscs twenty years after: What's new?

This research project by the Marine Biology Laboratory at Turin University determined the degree of conservation and measured the size of the Posidonia oceanica bed in the eastern Ligurian Sea off Punta Manara in 1985–1986, a bed that had also been examined in 1973. This project assessed the structure, dynamics, and organization of the foliar stratum malacofauna in relation to the most important space–time variables, the bathymetric gradients, and the seasons. In 2006 the laboratory investigated this bed with methods like the previous ones in order to evaluate the effect of anthropogenic disturbances and to assess any changes in the P. oceanica and mollusc-community dynamics. Our overall project has spanned many years, something unique in P. oceanica studies. Our structural analysis of the meadow found (i) a reduction in shoot density in all the bed's regions, particularly in the shallow and intermediate belts; (ii) a progressive reduction of the lower limit (now considered erosive–regressive). We sampled the foliar stratum molluscs using hand-towed nets, the means we used to collect semi-quantitative data. In 2006, there were 40% fewer specimens and 31.5% more species than in 1985–1986. The core-stock (sensu Russo) has remained the same over the years in terms of both the presence and the abundance of species (8 dominant species belonging to Cerithidae and Rissoidae). As in 1985–1986, Bittium latreillii is the dominant species, whose juveniles exhibited similar settlement dynamics on the foliar strata and whose samples had comparable peaks in reproduction and abundance. The multivariate approach was applied to both the 1985–1986 and the 2006 data set. The present results confirm those obtained through the Detrended Correspondence Analysis (DCA) in 1985–1986. Namely, time (the period or the season) is the main factor of variability, the one that influences the malacological assemblages the most. The composition of the stocks depends closely on the sampling period (ANOSIM, R=0.532, P<0.001) and hence is linked to the biological cycle of the seagrass. The development of P. oceanica affects the malacological assemblages and regulates them quantitatively, something most evident in the reproductive and settlement cycles of the two dominant families, Cerithidae and Rissoidae. Thus the spatial variations (the variations in depths or bathymetric gradient) play a major role in determining the species of the stocks, while the temporal variations – the changes in seasons – play a major role in determining the total number of molluscs.

Non-indigenous species in Mediterranean fish assemblages: Contrasting feeding guilds of Posidonia oceanica meadows and sandy habitats

Quantitative sampling in combination with classification of fish species into six major feeding guilds revealed the position and contribution of non-indigenous species (NIS) in the food web of Posidonia oceanica and sandy habitats in an area of the eastern Mediterranean. In P. oceanica beds and on sandy bottoms 10 and five species, respectively, were non-indigenous fish of Indo-Pacific origin. The proportional contribution of NIS individuals on P. oceanica beds was lower than that of sandy bottoms (12.7 vs. 20.4%) a pattern that also followed for biomass (13.6 vs. 23.4%), indicating that low diverse systems may be more liable to introductions than species-rich communities. The two habitats had similar fish feeding guilds, but the biomass contribution from NIS varied within each guild, indicating different degrees of impact on the available resources. This study showed that only few non-indigenous fish species contributed to the differences in biomass between habitats. No support could be found in postulating that taxonomic affiliation could predict invasion success. Size was considered highly important due to habitat shift of species with increased size. Two of the aspects considered in this study, the chance of establishing vs. the chance of being very dominant will depend upon competitive abilities strongly coupled to size and grounds for habitat shift. However, success of establishment will also depend on appropriate food resources in the recipient community as well as competitive abilities and level of competition in the food web within habitats.

Timing and habitat preferences for settlement of juvenile fishes in the Marine Protected Area of Torre Guaceto (south-eastern Italy, Adriatic Sea)

Timing and habitat preferences for settlement of juvenile fishes were investigated at the Marine Protected Area (MPA) of Torre Guaceto (SE Adriatic Sea) from April 2005 to March 2006. Data were obtained by visual census (on a fortnightly basis) in 10 habitat types identified within the depth range 0–6 m. A total of 22 taxa of juvenile fish was recorded: juveniles of 14 taxa were analysed for settlement timing and habitat preferences, whereas the other 8 taxa were only occasionally observed. Diplodus vulgaris and Sarpa salpa showed two settlement peaks, while the other 12 species displayed a single annual peak. Most species (10 out of 14) settled between late spring and early autumn. Juvenile labrids and Oblada melanura were mostly associated with exposed shallow rocks, while Diplodus sargus, D. vulgaris, D. puntazzo and S. salpa chiefly settled in shallow sheltered coves. Juveniles of Chromis chromis were found in sublittoral rocks and Posidonia oceanica beds. Spondilyosoma cantharus, Diplodus annularis and Dicentrarchus labrax mostly associated to P. oceanica and small-sized seagrasses for settlement, while Mullus surmuletus chiefly used sublittoral sands. This study provides evidence of clear coherence during settlement of many fishes in terms of habitat for settlement, while some discrepancy was found in terms of timing across the year. In addition, this study provided suggestive evidence of the potential of the MPA, relative to the habitats included within its borders, in hosting juvenile fish stages and thus contributing to sustain local diversity of the coastal fish fauna. Similar data would deserve to be properly considered to design MPAs and refine conservation targets.

Spatial and temporal patterns in Serranus cabrilla habitat use in the NW Mediterranean revealed by acoustic telemetry

We used acoustic telemetry to describe the spatial and temporal patterns of habitat use of one of the species most targeted by recreational anglers in the NW Mediterranean, Serranus cabrilla (Linnaeus, 1758). Temporal patterns and fish position were determined using a fixed-receiver array located in a marine protected area (MPA) in Palma Bay (Balearic Islands). Fish position as cen- tre of activity (COA, the centre of the area the fish uses during a specific time) and space utilisation preferences could be described due to a receiver array design with a high range detection overlap (more densely distributed near the COA). There were significantly more detections per time unit dur- ing the day, which was interpreted as increased activity possibly related to feeding habits and social behaviour. S. cabrilla spent 95% of its time in an average area of 0.77 ± 0.17 km 2 , with a core area (50% of the time) of 0.10 ± 0.29 km 2 . The home range size was not related to fish size or diel pattern (i.e. the size of the daytime home range was not significantly different from the night range). The lin- earity index and the index of reuse (proxies of site fidelity) also demonstrated that this species has high site fidelity, which suggests that it is sedentary with a limited adult dispersal capacity. Two main habitats were observed in the study area, and S. cabrilla spent on average much less time in seagrass meadows (Posidonia oceanica beds) compared to soft, gravel and detritus bottoms. A relatively small MPA would be a useful management tool for establishing sustainable exploitation levels of this species.

The first record of Cladocora caespitosa (Linnaeus, 1767) (Anthozoa, Scleractinia) from the Marmara Sea

The Scleractinian Cladocora caespitosa is reported for the first time from the Marmara Sea, Turkey. Five colonies of the elliptical Cladocora caespitosa were discovered at 7 m by scuba divers around Posidonia oceanica beds colonising a substrate of sand and rock. The colonies' characteristics were recorded with underwater apparatus with a close-up device and with a video system. The present paper provides the new updated area of the species on the Turkish coast.

Spatial pattern of coastal fish assemblages in different habitats in North‐western Mediterranean

AbstractVariability of fish assemblages across habitat structures can depend on spatial scales. A hierarchical sampling design was used to assess the spatial variability of temperate fish assemblages in different habitats and at multiple scales. Underwater visual censuses were carried out along the coasts of Elba Island (NW Mediterranean) on Posidonia oceanica beds, rocky algal reefs and sandy habitat at three spatial scales, namely tens of metres (individual replicates), hundreds of metres (sites) and tens of kilometres (locations). At the assemblage level, there was a clear relationship between fish and habitat type and the observed habitat‐related differences were largely dependent on species identity. Fish assemblages on P. oceanica beds and rocky reefs shared a high number of species, whereas overlap with sandy assemblages was negligible. Multivariate analyses revealed significant differences in fish assemblages among habitats, although there was also a significant habitat × site interaction. These differences relied mainly upon assemblage composition and species richness. Assemblages on rocky reefs and P. oceanica meadows usually harboured a higher number of species and individuals compared with sandy assemblages. Nevertheless, the patterns of habitat‐related differences in species richness and, especially, in the total number of fish, changed significantly from site to site. Eight species showed significant differences over habitats, but they were not consistent due to the interaction of habitat with site. Predictability of fish at both assemblage and population levels decreased with the scale of observation, and the spatial pattern of fish observed at the smallest scale was likely dependent on factors other than habitat type.

Relationships between multibeam backscatter, sediment grain size and Posidonia oceanica seagrass distribution

The use of data, including bathymetry, backscatter intensity and the angular response of backscatter intensity, collected using multibeam sonar (MBS) systems to recognise seabed types was evaluated in the inner shelf of central western Sardinia (western Mediterranean sea), a site characterised by a complex seabed including sandy and gravelly sediments, Posidonia oceanica seagrass beds growing on hardgrounds (i.e. biogenic carbonates) and sedimentary substrates. A MBS survey was carried out in order to collect bathymetric and acoustic backscatter data. Ground-truth data in the form of grab samples and diver observations were collected at 57 stations, 41 of which were in non-vegetated sedimentary substrate and 16 of which were in P. oceanica beds. Sediment samples were analysed for grain size. Statistical comparison between MBS backscatter and grain size data showed that backscatter intensity is strongly affected by sediment grain size, being directly correlated to the weight percent of the coarse fraction (1–16 mm) and inversely correlated to weight percent of the finer sediments (0.016–0.5 mm). Factor analysis of grain size and acoustic data identified three sedimentary facies: sandy gravels (SG), gravelly sands (GS) and slightly gravelly muddy sands (SGMS). Each facies showed different acoustic responses in terms of backscatter intensity and shape of the angular response curves. Differences in backscatter intensity among five seabed types, including the three sediment types identified by factor analysis and P. oceanica beds, growing on hardgrounds and sedimentary substrates, were tested by analysis of variance. P. oceanica on hardgrounds, P. oceanica on sedimentary substrates and GS exhibited values of relative backscatter intensity within the same range and, consequently, it was not possible to distinguish Posidonia beds and gravelly sands only on the basis of backscatter data. The similarity of backscatter intensity from P. oceanica growing on different substrates suggests that the acoustic response is mainly linked to the leaf canopy rather than the substrate it is growing on. A map of seabed classification, including sediment types and seagrass distribution was produced through a combination of information derived from backscatter data and morphological features derived from multibeam bathymetry, which were validated by ground-truth data.

Effects of marine cage aquaculture on macrofauna assemblages associated with Posidonia oceanica meadows

Marine cage aquaculture has the potential to severely impact Posidonia oceanica seagrass meadows and its associated fauna. In order to assess the impact of fish farming in a littoral bay of Corsica, France, physico-chemical (mud and organic matter) and biological (density and compactness of P. oceanica beds and associated macrofauna) variables have been examined in two stations putatively impacted to different degrees (St1 and St2) and in two unimpacted stations (Controls: C1 and C2). Principal Component Analysis of meadow structural variables (shoot density and compactness of matte) and abiotic variables (mud and organic matter percentage into sediment) highlighted differences among stations and, particularly, differences between impacted stations and controls. Results from C1 and C2 totally overlapped. St1 was the station which differed the most from controls. Compared with control stations, St1 and St2 were characterized by higher values of organic matter and mud and by lower values of shoot density and matte compactness. Permutational multivariate analysis of variance (PERMANOVA) did not show significant differences between C1 and C2 in the structure of macrofauna assemblages, whereas significant differences between the two impacted sites and between these and the control conditions emerged. Differences in assemblages were well correlated with the measured abiotic variables. The analysis showed that the species most responsible for difference among stations were typical of muddy sediment with high organic matter content. These species had higher mean abundance values at impacted stations than at controls. This study suggests fish farming determines an increase of organic matter and sedimentation, which resolve in changes in structural properties of the seagrass meadows and, consequently, changes in the associated macrofauna assemblages.

Modelling distribution patterns and habitat preference of the invasive green alga Caulerpa racemosa in the Saronikos Gulf (Eastern Mediterranean)

AB Aquatic Biology Contact the journal Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections AB 10:57-67 (2010) - DOI: https://doi.org/10.3354/ab00267 Modelling distribution patterns and habitat preference of the invasive green alga Caulerpa racemosa in the Saronikos Gulf (Eastern Mediterranean) Stelios Katsanevakis1,*, Maria Salomidi2, Aliki Panou3 1Institute of Marine Biological Resources, and 2Institute of Oceanography, Hellenic Centre for Marine Research, 46.7 km Athens-Sounio Avenue, 19013 Anavyssos, Greece 3Archipelagos – Environment and Development NGO, 28100 Lourthata, Kefalonia, Greece *Email: skatsan@ath.hcmr.gr or stelios@katsanevakis.com ABSTRACT: Although the invasive alga Caulerpa racemosa has exhibited an excessive rate of proliferation and has invaded the entire Mediterranean Sea basin within the last 18 yr, its spatial distribution patterns remain largely unknown. A 2-component modelling approach based on generalized additive models was applied to model the density of C. racemosa fronds in relation to spatial and environmental variables. A bimodal distribution of presence probability in relation to depth was observed, with higher probabilities of occurrence at very shallow bottoms (<4 m) and at depths between ~15 and 30 m. Presence probability steadily decreased at greater depths. Frond density was markedly higher in rocky habitats than in Posidonia oceanica beds or on sandy/muddy bottoms. The highest frond densities were observed in the southeastern part of the Saronikos Gulf, which is considered to be the area of initial establishment of the species in the Gulf; this indicates that time favours the steady expansion and further dominance of this species. KEY WORDS: Caulerpa racemosa · Generalized additive models · Greece · Invasive macrophytes · Spatial distribution patterns Full text in pdf format PreviousNextCite this article as: Katsanevakis S, Salomidi M, Panou A (2010) Modelling distribution patterns and habitat preference of the invasive green alga Caulerpa racemosa in the Saronikos Gulf (Eastern Mediterranean). Aquat Biol 10:57-67. https://doi.org/10.3354/ab00267 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in AB Vol. 10, No. 1. Online publication date: July 21, 2010 Print ISSN: 1864-7782; Online ISSN: 1864-7790 Copyright © 2010 Inter-Research.

Vulnerability of marine habitats to the invasive green alga Caulerpa racemosa var. cylindracea within a marine protected area

The relative vulnerability of various habitat types to Caulerpa racemosa var. cylindracea invasion was investigated in the National Marine Park of Zakynthos (Ionian Sea, Greece). The density of C. racemosa fronds was modelled with generalized additive models for location, scale and shape (GAMLSS), based on an information theory approach. The species was present in as much as 33% of 748 randomly placed quadrats, which documents its aggressive establishment in the area. The probability of presence of the alga within randomly placed 20 × 20 cm quadrats was 83% on ‘matte morte’ (zones of fibrous remnants of a former Posidonia oceanica bed), 69% on rocky bottoms, 86% along the margins of P. oceanica meadows, 10% on sandy/muddy substrates, and 6% within P. oceanica meadows. The high frond density on ‘matte morte’ and rocky bottoms indicates their high vulnerability. The lowest frond density was observed within P. oceanica meadows. However, on the margins of P. oceanica meadows and within gaps in fragmented meadows relative high C. racemosa densities were observed. Such gaps within meadows represent spots of high vulnerability to C. racemosa invasion.

Spatial variation in the composition of motile macroinvertebrate assemblages associated with two bed types of the seagrass Posidonia oceanica

The influence of continuous (non-fragmented) and reticulate (fragmented) bed type and plant architecture on the species richness, abundance and assemblage composition of motile macroinvertebrates associated with the seagrass Posidonia oceanica was investigated at 3 different spatial scales (10s of metres ('small'), 100s of metres ('medium') and kilometres ('large')). Univariate and multivariate analyses did not identify significant differences in the attributes of macroinverte- brate assemblages between the 2 P. oceanica bed types over the 3 spatial scales considered. On the other hand, significant spatial variation in macroinvertebrate attributes was detected at the large spa- tial scale. Results of univariate regression and multivariate correlation analysis consistently indicated significant relationships between attributes of the macroinvertebrate assemblages and epiphyte bio- mass at the large spatial scale. Although less consistent, significant relationships were also detected between attributes of the macroinvertebrate assemblages, and mean sediment grain size, total organic carbon in sediment and shoot biomass at the large and medium spatial scales. The findings indicate that naturally fragmented and non-fragmented P. oceanica beds have similar habitat charac- teristics for the associated macroinvertebrates and that local factors, which influence seagrass bed architecture and particularly epiphyte load, have greater influence on the seagrass fauna. Data from the present study support the notion that fragmented seagrass beds should receive the same atten- tion as non-fragmented ones with regard to habitat conservation and protection.

Occurrence and distribution of different bed types of seagrass Posidonia oceanica around the Maltese Islands

The small-scale distribution of Posidonia oceanica bed types were mapped at four locations off the northern coast of the Maltese Islands, using aerial photography supplemented by surveys using SCUBA diving. Results showed a similar pattern of occurrence of the seagrass at all locations surveyed. In shallow waters (2 m – 4 m), P. oceanicaoccurred as patches of variable size on a rocky and/or sandy substratum. In deeper waters (5 m – 10 m), the patches of seagrass were often replaced by reticulate beds consisting of P. oceanicainterspersed with areas of bare sand. Deeper still (11 m – 13 m), a transition from reticulate to continuous beds occurred. Continuous beds extended to depths of around 25 - 30 m and eventually became reticulate or patchy in deeper waters (&gt;25 m). Values of total seagrass percentage cover increased, while the ratio of fragmented:continuous bed cover decreased for the four study locations on moving southwards (Ramla Bay to St Thomas Bay), indicating that P. oceanica habitat was more abundant and less fragmented in the south-eastern parts of the Maltese Islands. However, values calculated using an exposure index did not did indicate a relationship between exposure and the observed decease in fragmentation of seagrass beds on moving northwest to southwest along the north-eastern coast. Data from the four sites surveyed, together with data from other surveys, were used to show the large-scale distribution of P. oceanica beds around the Maltese Islands. The implications of the study findings for the conservation and management of P. oceanica habitat around the Maltese Islands are discussed.

Seagrass light acclimation: 2-DE protein analysis in Posidonia leaves grown in chronic low light conditions

Posidonia oceanica meadows are among the most valuable coastal systems in the Mediterranean basin. They provide nursery and forage areas for many commercially important species, including juvenile mollusc, finfish, and crustaceans. In the Mediterranean Sea, P. oceanica beds have recently suffered from progressive die-offs attributed to lower light availability from elevated water turbidity. In order to understand adaptive low-light responses of this seagrass, we compared the protein expression in plants collected from turbid waters (low-light) with plants collected from pristine-clear waters (high-light). More than 2600 proteins were detected in leaves from both sites. Among them, 26 proteins were differentially expressed in low-light conditions, 12 of which were identified through MASCOT analyses. The remaining 14 proteins, did not receive significant identity scores due to a lack of genomic and proteomic information in available databases. Nevertheless, we observed a 30% down-regulation of RuBisCo large subunit in low-light acclimated leaves. Whereas, enzymes involved in carbohydrate cleavage (1-fructose-bisphosphate aldolase, nucleoside diphosphate kinase, and beta-amylase) were upregulated in low-light conditions. Electron microscopy studies also revealed substantial changes in the stroma lamellae/grana ratios in chloroplasts receiving low-light, possibly as a mechanism for re-establishing optimal PSI/PSII ratios. Furthermore, under low-light conditions, four components of the ubiquitin/mediated proteolysis pathway (26 S proteasome regulatory, proteasome beta type 1, proteasome 7 D beta type, and proteasome alpha 7), and the perchloric acid soluble translation inhibitor protein, were upregulated. This suggests that, in P. oceanica leaves, enhanced protein turnover mediates acclimation to low-light conditions. Also, enzymes involved in defending against cellular stress (superoxide dismutase, pyridoxine, and 2-caffeic-acido-methyl transferase) were differentially expressed in low-light regime. Subsequent aquaria studies involving P. oceanica transplants maintained in low- and high-light conditions, also demonstrate RuBisCo down-regulation and proteasomes upregulation in low-light acclimated plants.

Alterations of the structure of &lt;em&gt;Posidonia oceanica&lt;/em&gt; beds due to the introduced alga &lt;em&gt;Caulerpa taxifolia&lt;/em&gt;

The impact of Caulerpa taxifolia on the structure of shallow Posidonia oceanica beds was studied in permanent quadrats from 1995 to 2005 at the invaded site of Cap Martin and the control site of Cap d’Antibes (French Riviera, France). The cover of C. taxifolia , shoot density, number of orthotropic and plagiotropic shoots and proportion of ramifications of P. oceanica were measured yearly. The cover of C. taxifolia in the invaded zone rapidly reached a maximum of infestation in 2000 with 93% of the quadrats covered by the alga. In 2001 an unexplained phenomenon led to a sharp decrease in the infestation and in the following years the colonisation remained low. Within the 10 years of the study, P. oceanica did not disappear from the permanent quadrats, but we observed a drastic change in the structure of the meadow invaded by C. taxifolia . Between 1999 and 2000 a decrease in the shoot density observed at both sites was probably related to the warm temperature event recorded in 1999 (from 636 to 143 shoots m -2 at the invaded site and from 488 to 277 at the control site). At the invaded site, the seagrass never recovered its initial density even after a sharp decrease in C. taxifolia . The orthotropic/plagiotropic shoot ratio was strongly modified at the invaded site, where plagiotropic shoots became dominant because of an increase in their ramification.